Welding Alloy Steel

    Needless to say, with the large array of metals that modern mining has discovered or modern science refined from minerals which previously did not produce ore, many different steel alloys have been made. Many of these alloys are proprietary to a specific company, and there is such a huge number of possibilities that listing all of the current alloys would be a major study. The actual number of alloys which could be mixed probably approaches infinity.

    The uses of alloy steels are as varied as their composition. Most are purpose-made, with a certain suite of characteristics that makes them appropriate for a specific range of applications. The alloying metals (and occasional non-metallic materials) include nickel, chromium, silicon, boron, molybdenum, vanadium, aluminum, manganese, cobalt, tungsten, niobium, zirconium, and titanium, among many others.

    Many alloy steels will lose their desirable characteristics if they are overheated, so a light touch with the welding arc is advisable unless you have specific information to the contrary. There are several different categories of alloy steel, which each need their own special approach to be welded successfully.

Low-alloy steel, a.k.a. high-tensile steel

    With a typical alloy percentage of around 5%, and a maximum of 9%, low-alloy steel is corrosion resistant and can be hardened, as well as having around thrice the tensile strength of mild steel. Mild steel has a tensile strength of roughly 35 to 40 ksi (kilo-pounds per square inch), while the tensile strength of low-alloy steel is a minimum of 90 ksi and is usually much higher.

    For this reason, low-alloy steel is used for very rigorous applications that are subject to a lot of stress, including bridge girders, the structures of boats, truck frames, railway cars, and all kinds of heavy equipment. Weldability depends on the amount of carbon present in the low-alloy steel. If there a lot of carbon, the steel will be almost impossible to weld, while if carbon is low, then welding is fairly easy (although specific electrodes and filler metal, as well as special techniques, usually need to be applied).

High-strength low-alloy steel (HSLA steel) is the peak of low-alloy steels because of its extreme toughness and ease of welding.
 

Molybdenum steel
 

    This high-alloy, medium-carbon steel is used for aircraft and racer frames, and is fairly difficult to weld. You will need to cleanse the area around the weld joint of all surface oxides, and the pieces should be as close to 70° F as possible before welding begins. As with tool-and-die steels, great care must be taken lest the steel be overheated and lose its special traits.